I. Field of the Invention
The current invention relates to wireless communications. More particularly, the present invention relates to an improved method and system that requires decreased setup time in establishing a radio link protocol (RLP) data call.
II. Description of the Related Art
The use of code division multiple access (CDMA) modulation techniques is one of several techniques for facilitating communications in which a large number of system users are present. Other multiple access communication system techniques, such as time division multiple access (TDMA), frequency division multiple access (FDMA) and AM modulation schemes such as amplitude companded single sideband (ACSSB) are known in the art. These techniques have been standardized to facilitate interoperation between equipment manufactured by different companies. Code division multiple access communications systems have been standardized in the United States in Telecommunications Industry Association TIA/EIA/IS-95-B, entitled “MOBILE STATION-BASE STATION COMPATIBILITY STANDARD FOR DUAL-MODE WIDEBAND SPREAD SPECTRUM CELLULAR SYSTEMS”, incorporated by reference herein, and hereinafter referred to as IS-95. In addition, a new standard for Code division multiple access communications systems has been proposed in the United States in Telecommunications Industry Association PN-4431 to be published as TIA/EIA/IS-2000-5, entitled “UPPER LAYER (LAYER 3) SIGNALING STANDARD FOR cdma2000 SPREAD SPECTRUM SYSTEMS”, dated Jul. 11, 1999, incorporated by reference herein, and hereinafter referred to as IS-2000.
The International Telecommunications Union recently requested the submission of proposed methods for providing high rate data and high-quality speech services over wireless communication channels. A first of these proposals was issued by the Telecommunications Industry Association, entitled “The cdma2000 ITU-R RTT Candidate Submission.” A second of these proposals was issued by the European Telecommunications Standards Institute (ETSI), entitled “The ETSI UMTS Terrestrial Radio Access (UTRA) ITU-R RTT Candidate Submission”, also known as “wideband CDMA” and hereinafter referred to as W-CDMA. A third proposal was submitted by U.S. TG 8/1 entitled “The UWC-136 Candidate Submission”, hereinafter referred to as EDGE. The content of these submissions is public record and is well known in the art.
IS-95 was originally optimized for transmission of variable-rate voice frames. In order to support two-way voice communications, as typified in wireless phone applications, it is desirable that a communication system provides fairly constant and minimal data delay. For this reason, IS-95 systems are designed with powerful forward error correction (FEC) protocols and vocoders which are designed to respond gracefully to voice frame errors. Error control protocols which require frame retransmission procedures add unacceptable delays to voice transmission, so are not designed into the IS-95 specification.
The optimizations which make the standalone IS-95 specification ideal for voice applications make it difficult to use for packet data applications. In many non-voice applications, such as the transmission of Internet protocol (IP) data, the delay requirements of the communication system are much less stringent than in voice applications. In the Transmission Control Protocol (TCP), probably the most prevalent of protocols used in an IP network, virtually infinite transmission delays are allowed in order to guarantee error-free transmission. TCP uses retransmissions of IP datagrams, as IP packets are commonly called, to provide this transport reliability.
IP datagrams are generally too large to fit into a single IS-95 frame. Even after dividing an IP datagram into segments small enough to fit into a series of IS-95 frames, an entire series of IS-95 frames would have to be received without error for the single IP datagram to be useful to TCP. The frame error rate typical of an IS-95 system make the probability of error-free reception of all segments of a single datagram very low.
As described in IS-95, alternative service options enable the transmission of other types of data may in lieu of voice frames. The TIA/EIA/IS-707-A, entitled “DATA SERVICE OPTIONS FOR SPREAD SPECTRUM SYSTEMS”, hereafter referred to as IS-707, describes procedures used in the transmission of packet data in an IS-95 system.
Radio Link Protocol (RLP) is described in TIA/EIA/IS-707-A.8, entitled “DATA SERVICE OPTIONS FOR SPREAD SPECTRUM SYSTEMS: RADIO LINK PROTOCOL TYPE 2”, hereinafter referred to as RLP2, and incorporated herein by reference. RLP2 incorporates an error control protocol with frame retransmission procedures over the IS-95 frame layer. RLP is of a class of error control protocols known NAK-based ARQ protocols, which are well known in the art. The IS-707 RLP facilitates the transmission of a byte-stream, rather than a series of voice frames, through an IS-95 communication system.
Several protocol layers typically reside above the RLP layer. IP datagrams, for example, are typically converted into a Point-To-Point Protocol (PPP) byte stream before being presented as a byte stream to the RLP protocol layer. As the RLP layer ignores the protocol and framing of higher protocol layers, the stream of data transported by RLP is said to be a “featureless byte stream”.
RLP was originally designed to satisfy the requirements of sending large frames through an IS-95 channel. For example, if an IP datagram of 500 bytes were to be simply sent in IS-95 frames carrying 20 bytes each, the IP datagram would fill 25 consecutive IS-95 frames. Without some kind of error control layer, all 25 of these frames would have to be received without error in order for the IP datagram to be useful to higher protocol layers. On an IS-95 channel having a 1% frame error rate, the effective error rate of the IP datagram delivery would be (1−(0.99)25), or 22%. This is a very high error rate compared to most networks used to carry Internet Protocol traffic. RLP was designed as a link layer protocol which would decrease the error rate of IP traffic to be comparable to the error rate typical of a 10Base2 ethernet channel.
RLP is a negative acknowledgment (NAK) based protocol in which NAK frames are sent to prompt retransmission of data frames lost because of communication errors. The timing of NAK frame transmission is based on estimates of round-trip time (RTT) determined at the start of an RLP session. RTT determination in existing version of RLP requires a 3-way handshake in which both sides transmit specific frame types based on the frame types received. No data is sent by either side until the completion of the 3-way handshake. This 3-way handshake consumes time that could otherwise be used to transmit data.
In a typical data services configuration, a laptop computer is connected to a wireless modem that communicates with a network over an RLP connection. In a typical laptop computer application like browsing an Internet web page, the computer does not continuously exchange data with the network. Instead, the computer typically sends a short request for data containing the address of a web page. The wireless modem responds by establishing an RLP session with the local base station, and relays the request through the base station to the network. Through this RLP session, the wireless modem then receives the requested data (such as the contents of a web page), and displays the data for the user. While the user is reading the displayed data, no data is exchanged between the wireless modem and the base station or network.
In order to allow the most efficient use of wireless spectrum, a typical network employs “activity timers” that tear down an RLP session after a predetermined period of link inactivity. If this happens before the laptop computer attempts to send more data through the wireless modem, then another RLP session is established to service the new data. The re-establishing of a new RLP session causes additional delay in exchanging data with the network, which can be characterized by “sluggishness” of the laptop computer.
Bringing up a new RLP session to send new data will always take longer than sending the new data over an already-existing RLP session. Existing versions of RLP require the performance of a 3-way handshake to establish an RLP session. It is therefore highly desirable to minimize the overhead required to establish an RLP session, including minimizing or eliminating the delay inherent in the 3-way handshake.